110v tranny

[mickys86]

Bosch drill stopped working Friday afternoon, one min it was fine the next it wasn't. I've noticed recently that the transformer has been getting really hot when plugged in, even when nothing is plugged into the transformer.

So I take the top off and check the voltage going in.... 240 somat and the voltage coming out was only 59v? Get the fluke thermometer on it.... 47 degrees centigrade.

Being Friday afternoon I say it's a job for another day, gets another transformer plugs in drill and still doesn't work.
So it must be the drill? But what's with the heat and only the 59v?
I'm going to take a look at it soon but at the moment this is all I have time for

 

[derek preece]

Just out of interest, did you test between the earth and live conductor on the output as that should be in the region of 55V. Not sure about the excess heat.

 

[JUD]

Sounds like it's center tapped i.e. the secondary winding is center tapped to earth with 55V between each end of the winding and the center tap or 110V from one end of the winding to the other. Sounds like you're measuring the voltage between one end and the center tap.

 

[mickys86]

Ok that makes perfect sense now. 55v each side!
And now for the heat issue....

 

[sparkdog]

Sounds like shorted turns if getting hot with nothing plugged in.You will also find the primary current is excessive with shorted turns.

 

[mickys86]

Sounds like shorted turns if getting hot with nothing plugged in.You will also find the primary current is excessive with shorted turns.

So is this likely to cause a problem? Is it on its way out? Anything I can do to help it?

 

[sparkdog]

If its shorted turns nothing you can do except replace it.I suppose it might have been damaged if the drill is faulty.

 

[MarkieSparkie]

Transformer iron and hysteresis losses predominate at no-load and the transformer is most inefficient, this results in an unloaded transformer often running warmer than when supplying a small load, particularly where the designer has used minimal iron to reduce cost or size. However, as the load increases beyond a certain point copper losses progressively dominate and each doubling of the load current results in the copper losses quadrupling in proportion.